In general, a seat in a vehicle is a part for optimally maintaining the position of a passenger, and is largely composed of a seatback supporting the passenger's back and a seat cushion supporting the part of the passenger from the hip to the thigh.
The frame of the seat is composed of a seat cushion frame and a seatback frame and a reclining device is provided to the connecting portion of the seat cushion frame and the seatback frame to adjust the angle of the seatback forward/backward according to the shape of the passenger's body.
The reclining device is composed of a pair of parts that is provided to the left and right sides of the seat, and the two reclining devices each are fitted to both ends of a shaft by a spline.
The reclining device is divided into an electric type that performs reclining while rotated by a driving force of an electric motor and a manual type that performs reclining while rotated by passenger's operation of a lever, and the manual type is described herein.
Further, the reclining device should have a strong engagement force between geared parts to improve the entire strength and prevent an erroneous operation.
It is preferable to increase the size of the reclining device in order to increase the engagement force between the geared parts, but it is difficult to unlimitedly increase the size of the reclining device because the size is determined in consideration of the size of the seat.
Accordingly, according to the reclining device in the related art, the sector tooth and the pawl tooth are forcibly disengaged by the load applied to the seatback by the passenger in a car collision, and as a result the seatback unexpectedly pivots and the passenger's safety is threatened.